So the Qts is similar, leading both boxes to be suitable for bass reflex and sealed alignment.

I read this thread, casting doubt on the importance of Qms and Qes in isolation, unless you have a high output impedance amplifier (eg a Valve based design)

I don't know much about speaker design in practice but I would imagine that Qes based damping is more linear, assuming the magnetic field is even, and mechanical damping is almost always the higher of the two coefficients making up Qts.

I am trying to protect my Quad ESL 63's from to much bass demands without compromising sound quality significantly. What draws me to this driver is probably mostly marketing. I am really looking for some thing with no large resonances in the frequency response up to 1Khz, low harmonic distortion, and some lowish bass.

Experiments with a 100Hz, 24db / Octave op amp based low pass filter, showed that this still is effecting the Quad midrange with the Linn Helix bass reflex mid bass speakers I have. For this reason in particular I don't want high frequency harmonics generated by the bass driver or speaker box.

I am thinking that the bass filter may benefit from a second step at a higher frequency than my target cross over in the 100Hz region. Maybe with a 2nd or 4th order crossover in addition at around 300 hz.

As you can see I am a beginner so have many questions and ideas and hopefully will make a solution good enough to save me applying too many ideas.

Could you expand a little on your experiments with 24dB/octave filters? My tapped horns have some upper bass peaks that are tamed with a 24dB/oct filter (see my signature), so I'm more than a little curious about why this wasn't so for you.

Some of the usual I-want-to-make-a-subwoofer questions:
- how loud do you want it to go?
- how low do you want it to go?
- what will you use to power it?
- what's the budget?
- how big can the cabinet be?

If you haven't already, download winISD Pro and follow the help section on how to input the T/S parameters of a driver. Then you can start playing around with cabinet volume, ported/sealed, etc.
My thoughts would be a ~50L cabinet tuned to 30Hz - that'll go low enough for most music, and the Visaton's large excursion means decent output levels, too. A sealed cabinet with some boost in the low end could reach lower, but excursion gets used up fast: I wouldn't consider an 8" driver per side sufficient for really low bass, based on my own experiences (2x8" drivers, equilised to 28Hz).

For my own position I should state that the ESL 63's have enough bass for me for most of the time, just not always. I don't want to over drive the elctrostatic speakers when playing movies or reggae/electronic music. The subwoofer is mostly a way to boost the resilience and add bass to the party (including better sound slightly off axis), especially when playing a sound far louder than expected, which does happen. My current set up with a 100Hz cross over does provide a considerable confidence factor, that I wont have to get my speakers repaired.

Quote:

Originally Posted by chris661

Could you expand a little on your experiments with 24dB/octave filters? My tapped horns have some upper bass peaks that are tamed with a 24dB/oct filter (see my signature), so I'm more than a little curious about why this wasn't so for you.

As you may know the Quad ESL 63 has rather amazing stereo imaging. After playing with a 12db/oct variable cross over I found 100Hz was approximately the highest frequency I could use without effecting the stereo imaging to much. (and about the point the ESL 63 seems on measurements I have seen on the web, to start showing much less linear frequency response)

When I first made up a fixed frequencies cross over with the 100Hz, 24dB/oct cross over, I noticed a significant improvement over the variable cross over, particularly in stereo imaging. I was very happy, then later I reorganized the wiring a little. After a few weeks/months, I noticed the stereo imaging was slightly degraded, only later did I realize the bass speakers where wired left under the right and right under the left, after I fixed this things where better.

With my current implementation, things are really quiet good, but I did notice the stereo image for where the midrange was coming from seemed to drop about 5-10 cm down from the center of the ESL speaker with the 100Hz, 24dB/oct cross over with the Linn speakers under the ESL 63's engaged, and return to the middle of the ESL with the Bass unit unplugged.

As I cant measure the audio frequency response (I do want a measurement microphone) I am unaware of the bass cut off of the Linn Helix speakers but I would not be surprised (considering the shortness of the reflex slot and its width), that it might well be in the 50-80 Hz region. If anyone knows how to calculate the slot bass resonant frequency of my Linn Helix speakers I would be interested to know what it is. (140 mm length, 190 mm wide, 25mm high, tapering to 20mm high on inside.)

Also playing at excessively loud volumes (middle of day on a Saturday so as not to annoy the neighbors) I could easily hear some midrange coming through the bass units, allowing easy localisation, when the Quad ESL 63's where switched off.

Since these experiments I am quiet sure that I need to be careful to keep the ESL 63's magic in stereo imaging, and crossing as high as 100 Hz is around the upper limit for this, and I fear higher frequency harmonics may intrude to greatly.

Quote:

Originally Posted by chris661

Some of the usual I-want-to-make-a-subwoofer questions:
- how loud do you want it to go?

Using my osciliscope on the amplifier input, ESL 63's 5V peak on 6 Ohm seemed plenty loud, and any louder would be rare so looking at the specs this is around 92dB. Maybe on rare occasions I would like a little more. Lets say a realistic peak number of around 95dB

Quote:

Originally Posted by chris661

- how low do you want it to go?

Not yet sure but I think 40 Hz -3dB is a fair target but its not set in stone. I am not convinced that you can go much lower than this with out paying all sorts of money, distortion and complexity, compromises, which will possibly not match nicely with the electrostatic's clarity.

If this proves annoying after a year I may consider another upgrade of a separate real low subwoofer, but the expectation is that this will be less distortion sensitive as at 100Hz -3dB already the Bass localisation is significantly reduced.

Quote:

Originally Posted by chris661

- what will you use to power it?

I have a 2 Quad 306's (30V 6 amp) and 3 Quad 303 (30 V 3 Amp) the 303, (or my sugden A28 which is better, or a class A of my own making) will drive the ESL's and the pair of 306's could drive the bass.

Quote:

Originally Posted by chris661

- what's the budget?

Well I would budget for 2 boxes to be built minimum as things will need being remade after I have finished experimenting. so thats going to cost in the region of 150 Euro for the final box and 50 Euro per test box, as for the drivers, I am thinking about 200 Euro per side maximum.

Giving a maximum cost for hardware, around 600 Euro the pair including box prototypes.

Quote:

Originally Posted by chris661

- how big can the cabinet be?

Well smaller is better as I dont think I will die in this house. The maximum size is about 300 mm high (220 - 250mm preferred as high makes the ESL's a little two high as the rotational bass is 80mm high and an extra 30 mm feet would be liked.), 600 mm wide (600 mm strongly preferred to match the ESL's and the platform though is could bulge in the middle), and 600 mm deep (250 mm preferred as it would then fit under the ESL with no bulge). This said since I no longer live in the UK I have a bigger house than I am used to, that said I woudl pay a little extra for smaller, which is an attraction.

Quote:

Originally Posted by chris661

If you haven't already, download winISD Pro and follow the help section on how to input the T/S parameters of a driver. Then you can start playing around with cabinet volume, ported/sealed, etc.

My thoughts would be a ~50L cabinet tuned to 30Hz - that'll go low enough for most music, and the Visaton's large excursion means decent output levels, too. A sealed cabinet with some boost in the low end could reach lower, but excursion gets used up fast: I wouldn't consider an 8" driver per side sufficient for really low bass, based on my own experiences (2x8" drivers, equilised to 28Hz).

I must admit the idea of 2X8" drivers has a strong appeal (except for cost), both as a staged second upgrade, and to remove fear that the rotating platform the speakers will sit on will effect the Bass, I can also easily see myself equalizing the bass drivers to extend low response by an octave if they are in a sealed box, with no lower frequency sub woofer to help them out. The Contrapunt, a dipole sub woofer also resolves this issue as each speaker would be equally off axis and so prevent rotation, but it does look like with the rotating platform it will be a little two wide (I could make it it a little wider in the middle and bring the top and bottom in) and also a bit high, the height issue is not easily solvable.

I am also particularly keen to hear experiences of the Visaton TIW200XS as both a subwoofer and as a midbass unit.

For my own position I should state that the ESL 63's have enough bass for me for most of the time, just not always. I don't want to over drive the elctrostatic speakers when playing movies or reggae/electronic music. The subwoofer is mostly a way to boost the resilience and add bass to the party (including better sound slightly off axis), especially when playing a sound far louder than expected, which does happen. My current set up with a 100Hz cross over does provide a considerable confidence factor, that I wont have to get my speakers repaired.

I know exactly what you mean - mechanical damage is something to avoid wherever possible. In this respect, it's completely understandable as to why you'd want to add woofers.

Quote:

Originally Posted by owenhamburg

As you may know the Quad ESL 63 has rather amazing stereo imaging. After playing with a 12db/oct variable cross over I found 100Hz was approximately the highest frequency I could use without effecting the stereo imaging to much. (and about the point the ESL 63 seems on measurements I have seen on the web, to start showing much less linear frequency response)

When I first made up a fixed frequencies cross over with the 100Hz, 24dB/oct cross over, I noticed a significant improvement over the variable cross over, particularly in stereo imaging. I was very happy, then later I reorganized the wiring a little. After a few weeks/months, I noticed the stereo imaging was slightly degraded, only later did I realize the bass speakers where wired left under the right and right under the left, after I fixed this things where better.

With my current implementation, things are really quiet good, but I did notice the stereo image for where the midrange was coming from seemed to drop about 5-10 cm down from the center of the ESL speaker with the 100Hz, 24dB/oct cross over with the Linn speakers under the ESL 63's engaged, and return to the middle of the ESL with the Bass unit unplugged.

It sounds like the Linns are still leaking a little midrange through. It might not sound like much, but dropping the crossover frequency to more like 80Hz (remember it's nearly half an octave in the bass) will cut the midrange output some more. And yes, having heard some ESLs (think they were 63s), keeping that magic is of importance.

Quote:

Originally Posted by owenhamburg

As I cant measure the audio frequency response (I do want a measurement microphone) I am unaware of the bass cut off of the Linn Helix speakers but I would not be surprised (considering the shortness of the reflex slot and its width), that it might well be in the 50-80 Hz region. If anyone knows how to calculate the slot bass resonant frequency of my Linn Helix speakers I would be interested to know what it is. (140 mm length, 190 mm wide, 25mm high, tapering to 20mm high on inside.)

Commercial speakers are often misaligned to give a peak in the midbass, instead of solid low frequency output. To figure out the port tuning, we'll need cabinet volume and port dimensions - I'm not exactly sure what the dimensions are you've given ( a quick sketch is often useful in these situations).

Quote:

Originally Posted by owenhamburg

Also playing at excessively loud volumes (middle of day on a Saturday so as not to annoy the neighbors) I could easily hear some midrange coming through the bass units, allowing easy localisation, when the Quad ESL 63's where switched off.

Since these experiments I am quiet sure that I need to be careful to keep the ESL 63's magic in stereo imaging, and crossing as high as 100 Hz is around the upper limit for this, and I fear higher frequency harmonics may intrude to greatly.

Any subwoofer at all will bleed a little midrange through when the rest of the system is switched off. Ears are incredibly insensitive to low frequencies, so even if the midrange is 50dB down coming out the speakers, it will still be noticable. Have a look at Fletcher-Munson curves for more.

Quote:

Originally Posted by owenhamburg

Using my osciliscope on the amplifier input, ESL 63's 5V peak on 6 Ohm seemed plenty loud, and any louder would be rare so looking at the specs this is around 92dB. Maybe on rare occasions I would like a little more. Lets say a realistic peak number of around 95dB

Not yet sure but I think 40 Hz -3dB is a fair target but its not set in stone. I am not convinced that you can go much lower than this with out paying all sorts of money, distortion and complexity, compromises, which will possibly not match nicely with the electrostatic's clarity.

The numbers you've given are certainly feasible with these drivers. I'd still suggest you could go lower with the available air displacement, but, as you rightly say, keeping excursion smaller will reduce distortion. In a cabinet tuned to 30Hz, a single 8" driver needs 3mm one-way travel to do 95dB at 40Hz. When you consider that the excursion requirement would drop to 1.5mm one-way displacement (ie, 3mm p/p) for a pair of drivers, I think you could get away with this: these are, after all, subwoofer drivers designed for considerable movement before distortion. Still, this is your project - I just think you could go 10Hz lower without any serious penalty apart from cabinet size.

Quote:

Originally Posted by owenhamburg

If this proves annoying after a year I may consider another upgrade of a separate real low subwoofer, but the expectation is that this will be less distortion sensitive as at 100Hz -3dB already the Bass localisation is significantly reduced.

I have a 2 Quad 306's (30V 6 amp) and 3 Quad 303 (30 V 3 Amp) the 303, (or my sugden A28 which is better, or a class A of my own making) will drive the ESL's and the pair of 306's could drive the bass.

These will be more than sufficient - just wanted to make sure you're not planning on using a valve amp: these often have an output impedance of a couple of ohms, which can affect bass response (play with series resistance added in winISD).

Quote:

Originally Posted by owenhamburg

Well I would budget for 2 boxes to be built minimum as things will need being remade after I have finished experimenting. so thats going to cost in the region of 150 Euro for the final box and 50 Euro per test box, as for the drivers, I am thinking about 200 Euro per side maximum.

Giving a maximum cost for hardware, around 600 Euro the pair including box prototypes.

This ought to be plenty, I can't see any problems arising here.

Quote:

Originally Posted by owenhamburg

Well smaller is better as I dont think I will die in this house. The maximum size is about 300 mm high (220 - 250mm preferred as high makes the ESL's a little two high as the rotational bass is 80mm high and an extra 30 mm feet would be liked.), 600 mm wide (600 mm strongly preferred to match the ESL's and the platform though is could bulge in the middle), and 600 mm deep (250 mm preferred as it would then fit under the ESL with no bulge). This said since I no longer live in the UK I have a bigger house than I am used to, that said I woudl pay a little extra for smaller, which is an attraction.

I'm personally not so keen on the idea of dipole bass systems. For me, there is a lot of wasted potential in the drivers: one system I heard had a 15" midbass and a pair of 18" woofers per side. Sure, it went fairly loud and fairly low. But you could get lower, louder, (dare I say it) cleaner bass out of them if they had adequate cabinet loading. For a domestic system, the huge driver requirements put me off.

Quote:

Originally Posted by owenhamburg

I must admit the idea of 2X8" drivers has a strong appeal (except for cost), both as a staged second upgrade, and to remove fear that the rotating platform the speakers will sit on will effect the Bass, I can also easily see myself equalizing the bass drivers to extend low response by an octave if they are in a sealed box, with no lower frequency sub woofer to help them out. The Contrapunt, a dipole sub woofer also resolves this issue as each speaker would be equally off axis and so prevent rotation, but it does look like with the rotating platform it will be a little two wide (I could make it it a little wider in the middle and bring the top and bottom in) and also a bit high, the height issue is not easily solvable.

I am also particularly keen to hear experiences of the Visaton TIW200XS as both a subwoofer and as a midbass unit.

Regards

Owen

Bass output is omnidirectional - you'll get equal bass output no matter which way the drivers are pointing, as the wavelengths are so long they "wrap" around the cabinet, spreading evenly in the room.

If you wanted to experiment, having a blockable port (using draught-excluder and a piece of wood screwed to the cabinet works nicely, but it's not pretty) would allow you to try sealed vs ported cabinets. You could also try stuffing/lining the cabinets.

I am thinking that the bass filter may benefit from a second step at a higher frequency than my target cross over in the 100Hz region. Maybe with a 2nd or 4th order crossover in addition at around 300 hz.

Hi Owen,

Here is a suggestion I think would work well as long as you don't place a sub near your Quad ESL 63's but instead use a centrally position or even at the rear wall.

b

PS: In the sixties I owned a pair of Quad ESL 57's.Remember that I too had a problem to extend the lower end frequencies and failed when trying to use monopole subs as stands for the ESL's.